Electro-optic displays with touch sensors and/or tactile feedback

ABSTRACT

An electro-optic display comprises, in order, a light-transmissive electrically-conductive layer; a layer of a solid electro-optic material; and a backplane ( 162 ) bearing a plurality of pixel electrodes. A peripheral portion of the backplane extends outwardly beyond the layer of solid electro-optic material and bears a plurality of radiation generators ( 166 ) and a plurality of radiation detectors ( 168 ), the radiation generators and detectors together being arranged to act as a touch screen.

REFERENCE TO RELATED APPLICATIONS

This application claims benefit of copending Application Ser. No.61/255,580, filed Oct. 28, 2009.

This application is related to:

-   -   (a) U.S. Pat. Nos. 6,473,072 and 6,738,050;    -   (b) U.S. Pat. Nos. 7,030,854; 7,312,784; and 7,705.824;    -   (c) U.S. Pat. No. 6,392,786;    -   (d) U.S. Pat. No. 7,110,164; and    -   (e) U.S. Pat. Nos. 6,473,072 and 6,738,050.

The entire contents of these patents and application, and of all otherU.S. patents and published and copending applications mentioned below,are herein incorporated by reference.

BACKGROUND OF INVENTION

This application relates to electro-optic displays provided with touchsensors and/or tactile feedback. This invention is primarily directed tosuch electro-optic displays which use solid electro-optic media, as thatterm is defined below.

The term “electro-optic”, as applied to a material, medium or a display,is used herein in its conventional meaning in the imaging art to referto a material having first and second display states differing in atleast one optical property, the material being changed from its first toits second display state by application of an electric field to thematerial. Although the optical property is typically color perceptibleto the human eye, it may be another optical property, such as opticaltransmission, reflectance, luminescence or, in the case of displaysintended for machine reading, pseudo-color in the sense of a change inreflectance of electromagnetic wavelengths outside the visible range.

Some electro-optic materials are solid in the sense that the materialshave solid external surfaces, although the materials may, and often do,have internal liquid- or gas-filled spaces. Such displays using solidelectro-optic materials may hereinafter for convenience be referred toas “solid electro-optic displays”. Thus, the term “solid electro-opticdisplays” includes rotating bichromal member displays, encapsulatedelectrophoretic displays, microcell electrophoretic displays andencapsulated liquid crystal displays.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin U.S. Pat. No. 7,170,670 that some particle-based electrophoreticdisplays capable of gray scale are stable not only in their extremeblack and white states but also in their intermediate gray states, andthe same is true of some other types of electro-optic displays. Thistype of display is properly called “multi-stable” rather than bistable,although for convenience the term “bistable” may be used herein to coverboth bistable and multi-stable displays.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedby applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display uses an electrochromic medium, forexample an electrochromic medium in the form of a nanochromic filmcomprising an electrode formed at least in part from a semi-conductingmetal oxide and a plurality of dye molecules capable of reversible colorchange attached to the electrode; see, for example O'Regan, B., et al.,Nature 1991, 353, 737; and Wood, D., Information Display, 18 (3), 24(March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14 (11),845. Nanochromic films of this type are also described, for example, inU.S. Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of mediumis also typically bistable.

Another type of electro-optic display is an electro-wetting displaydeveloped by Philips and described in Hayes, R. A., et al., “Video-SpeedElectronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003).It is shown in U.S. Pat. No. 7,420,549 that such electro-wettingdisplays can be made bistable.

Another type of electro-optic display, which has been the subject ofintense research and development for a number of years, is theparticle-based electrophoretic display, in which a plurality of chargedparticles move through a fluid under the influence of an electric field.Electrophoretic displays can have attributes of good brightness andcontrast, wide viewing angles, state bistability, and low powerconsumption when compared with liquid crystal displays. Nevertheless,problems with the long-term image quality of these displays haveprevented their widespread usage. For example, particles that make upelectrophoretic displays tend to settle, resulting in inadequateservice-life for these displays.

As noted above, electrophoretic media require the presence of a fluid.In most prior art electrophoretic media, this fluid is a liquid, butelectrophoretic media can be produced using gaseous fluids; see, forexample, Kitamura, T., et al., “Electrical toner movement for electronicpaper-like display”, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y.,et al., “Toner display using insulative particles chargedtriboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also U.S. Pat.Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic mediaappear to be susceptible to the same types of problems due to particlesettling as liquid-based electrophoretic media, when the media are usedin an orientation which permits such settling, for example in a signwhere the medium is disposed in a vertical plane. Indeed, particlesettling appears to be a more serious problem in gas-basedelectrophoretic media than in liquid-based ones, since the lowerviscosity of gaseous suspending fluids as compared with liquid onesallows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporationdescribe various technologies used in encapsulated electrophoretic andother electro-optic media. Such encapsulated media comprise numeroussmall capsules, each of which itself comprises an internal phasecontaining electrophoretically-mobile particles in a fluid medium, and acapsule wall surrounding the internal phase. Typically, the capsules arethemselves held within a polymeric binder to form a coherent layerpositioned between two electrodes. The technologies described in thethese patents and applications include:

-   -   (a) Electrophoretic particles, fluids and fluid additives; see        for example U.S. Pat. Nos. 7,002,728 and 7,679,814;    -   (b) Capsules, binders and encapsulation processes; see for        example U.S. Pat. Nos. 6,922,276 and 7,411,719;    -   (c) Films and sub-assemblies containing electro-optic materials;        see for example U.S. Pat. No. 6,982,178 and U.S. Patent        Application Publication No. 2007/0109219;    -   (d) Backplanes, adhesive layers and other auxiliary layers and        methods used in displays; see for example U.S. Pat. Nos.        D485,294; 6,124,851; 6,130,773; 6,177,921; 6,232,950; 6,252,564;        6,312,304; 6,312,971; 6,376,828; 6,392,786; 6,413,790;        6,422,687; 6,445,374; 6,480,182; 6,498,114; 6,506,438;        6,518,949; 6,521,489; 6,535,197; 6,545,291; 6,639,578;        6,657,772; 6,664,944; 6,680,725; 6,683,333; 6,724,519;        6,750,473; 6,816,147; 6,819,471; 6,825,068; 6,831,769;        6,842,167; 6,842,279; 6,842,657; 6,865,010; 6,967,640;        6,980,196; 7,012,735; 7,030,412; 7,075,703; 7,106,296;        7,110,163; 7,116,318; 7,148,128; 7,167,155; 7,173,752;        7,176,880; 7,190,008; 7,206,119; 7,223,672; 7,230,751;        7,256,766; 7,259,744; 7,280,094; 7,327,511; 7,349,148;        7,352,353; 7,365,394; 7,365,733; 7,382,363; 7,388,572;        7,442,587; 7,492,497; 7,535,624; 7,551,346; 7,554,712;        7,583,427; 7,598,173; 7,605,799; 7,636,191; 7,649,674;        7,667,886; 7,672,040; 7,688,497; 7,733,335; and 7,785,988; and        U.S. Patent Applications Publication Nos. 2002/0060321;        2004/0105036; 2004/0180476; 2005/0122306; 2005/0122563;        2007/0052757; 2007/0085818; 2007/0097489; 2007/0109219;        2007/0211002; 2008/0211765; 2009/0122389; 2009/0225397;        2009/0231661; 2009/0315044; 2010/0039697; 2010/0039706;        2010/0118384; 2010/0165446; and 2010/0265239; International        Application Publication No. WO 00/38000; European Patents Nos.        1,099,207 B1 and 1,145,072 B1;    -   (e) Color formation and color adjustment; see for example U.S.        Pat. No. 7,075,502 and U.S. Patent Application Publication No.        2007/0109219;    -   (f) Methods for driving displays; see for example U.S. Pat. Nos.        7,012,600 and 7,453,445;    -   (g) Applications of displays; see for example U.S. Pat. No.        7,312,784 and U.S. Patent Application Publication No.        2006/0279527; and    -   (h) Non-electrophoretic displays, as described in U.S. Pat. Nos.        6,241,921; 6,950,220; and 7,420,549; and U.S. Patent Application        Publication No. 2009/0046082.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display, inwhich the electrophoretic medium comprises a plurality of discretedroplets of an electrophoretic fluid and a continuous phase of apolymeric material, and that the discrete droplets of electrophoreticfluid within such a polymer-dispersed electrophoretic display may beregarded as capsules or microcapsules even though no discrete capsulemembrane is associated with each individual droplet; see for example,the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes ofthe present application, such polymer-dispersed electrophoretic mediaare regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to SipixImaging, Inc.

Although electrophoretic media are often opaque (since, for example, inmany electrophoretic media, the particles substantially blocktransmission of visible light through the display) and operate in areflective mode, many electrophoretic displays can be made to operate ina so-called “shutter mode” in which one display state is substantiallyopaque and one is light-transmissive. See, for example, U.S. Pat. Nos.5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and6,184,856. Dielectrophoretic displays, which are similar toelectrophoretic displays but rely upon variations in electric fieldstrength, can operate in a similar mode; see U.S. Pat. No. 4,418,346.Other types of electro-optic displays may also be capable of operatingin shutter mode.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating; meniscus coating; spin coating; brush coating; air knifecoating; silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink jet printing processes;electrophoretic deposition (See U.S. Pat. No. 7,339,715); and othersimilar techniques.) Thus, the resulting display can be flexible.Further, because the display medium can be printed (using a variety ofmethods), the display itself can be made inexpensively.

Other types of electro-optic media may also be used in the displays ofthe present invention.

U.S. Pat. No. 6,982,178 describes a method of assembling a solidelectro-optic display (including an encapsulated electrophoreticdisplay) which is well adapted for mass production. Essentially, thispatent describes a so-called “front plane laminate” (“FPL”) whichcomprises, in order, a light-transmissive electrically-conductive layer;a layer of a solid electro-optic medium in electrical contact with theelectrically-conductive layer; an adhesive layer; and a release sheet.Typically, the light-transmissive electrically-conductive layer will becarried on a light-transmissive substrate, which is preferably flexible,in the sense that the substrate can be manually wrapped around a drum(say) 10 inches (254 mm) in diameter without permanent deformation. Theterm “light-transmissive” is used in this patent and herein to mean thatthe layer thus designated transmits sufficient light to enable anobserver, looking through that layer, to observe the change in displaystates of the electro-optic medium, which will normally be viewedthrough the electrically-conductive layer and adjacent substrate (ifpresent); in cases where the electro-optic medium displays a change inreflectivity at non-visible wavelengths, the term “light-transmissive”should of course be interpreted to refer to transmission of the relevantnon-visible wavelengths. The substrate will typically be a polymericfilm, and will normally have a thickness in the range of about 1 toabout 25 mil (25 to 634 μm), preferably about 2 to about 10 mil (51 to254 μm). The electrically-conductive layer is conveniently a thin metalor metal oxide layer of, for example, aluminum or ITO, or may be aconductive polymer. Poly(ethylene terephthalate) (PET) films coated withaluminum or ITO are available commercially, for example as “aluminizedMylar” (“Mylar” is a Registered Trade Mark) from E.I. du Pont de Nemours& Company, Wilmington Del., and such commercial materials may be usedwith good results in the front plane laminate.

Assembly of an electro-optic display using such a front plane laminatemay be effected by removing the release sheet from the front planelaminate and contacting the adhesive layer with the backplane underconditions effective to cause the adhesive layer to adhere to thebackplane, thereby securing the adhesive layer, layer of electro-opticmedium and electrically-conductive layer to the backplane. This processis well-adapted to mass production since the front plane laminate may bemass produced, typically using roll-to-roll coating techniques, and thencut into pieces of any size needed for use with specific backplanes.

It is known (see the patents and application mentioned in the “Referenceto Related Applications section above) to provide electro-optic displayswith touch screens. Many display applications benefit from touchsensitivity. In many cases, touch sensitivity in a limited number offixed areas can be used for elements of the user interface.Alternatively, applications such as drawing, underlining, or complex andchangeable user interfaces benefit from a full touch screen. Touchsensing capabilities also offer the possibility of producing anelectronic paper-like display which mimics not only the readability butalso the writeability of conventional paper. The ability to detect, atfrequent intervals, the position of a finger or stylus on a displayscreen, enables a display to use the position information to effectselection of menu items or to capture handwriting as “digital ink”.

Although touch sensing is not strictly a display function, the touchsensor is typically considered part of the display because it must beco-located with the display (either above or below the display surface).Unfortunately, most touch screen technologies are not suitable for usewith portable products using electrophoretic displays. Of the types oftouch screen which are inexpensive, compact, and sufficiently low inpower demand to address such displays, many require multiple layersand/or interfaces to be stacked on top of the display medium. Sinceelectrophoretic displays are reflective, optical performance is reducedby each additional layer and interface interposed between theelectro-optic layer and the user. Many types of touch screen also addexcessive thickness to the display stack, and require multipleadditional processing steps to form the complete display panel.

Inductive touch screens can be placed behind the backplane layer (i.e.,on the opposed side of the backplane to both the user and theelectro-optic medium), and thus do not affect optical performance. Suchinductive touch screens also add minimal thickness, but they areexpensive and require use of a special stylus.

Surface capacitive touch screens are a promising avenue for use withelectro-optic displays. This type of touch screen is typically laminatedor positioned over the front of a finished display. As shown in FIG. 1Aof the accompanying drawings, a typical form of such a touch screen hasa substrate 1, typically formed of poly(ethylene terephthalate) (PET)having a thickness in the range of about 50 to about 250 μm. Alight-transmissive, electrically-conductive layer 2 is formed on thesurface of the substrate 1. The layer 2 may be formed of indium tinoxide (ITO) or any other light-transmissive electrical conductor, forexample PEDOT, carbon nanotubes or other inorganic conductors. The touchscreen actually works better if the resistance of the layer 2 is not toolow, a preferred range being about 1 to 5 Kohm/square, a range which canbe achieved by ITO or various polymeric conductors. A low sheetresistance material 3 (typically screen printed silver ink) is formedand patterned in contact with the conductive layer 2. As discussedbelow, the various parts of the material 3 serve several functions.

As illustrated in FIG. 1B, the material 3 includes corner electrodes 4that make good electrical contact with the corners of the layer 2 andwhich are in electrical contact with a touch screen controller (notshown) via connector points 6. The corner electrodes 4 are the primarypoints the controller uses to inject measurement signals and sensechanges in capacitance in order to detect touches on the screen. Thematerial 3 also provides a linearization pattern 5, which selectivelyshorts out sections at the edges of the sheet conductor and causes theelectrical field distribution to spread out over the screen morelinearly than it otherwise would. Without the pattern 5, the electricalfield would be subject to severe pincushion distortion and it would bedifficult to implement a useful touch sensor. The connector points 6are, as already noted, used to form connections from the touch screen tothe controller; usually, these connections are provided in the form of asmall flexible circuit tail ΛCF or conductive adhesive bonded to theconnector points 6. Finally, the material 3 forms a proximity sensingelectrode 7, which is needed in small surface capacitance screen todetect when a user approaches the screen. The proximity sensingelectrode 7 can be a ring electrode encircling the screen, asillustrated in FIG. 1B, or may be formed as a separate layer (forexample, an aluminized polymeric film in the form of a die cut ring)laminated to the peripheral portion of the screen to reduce thefootprint of the touch sensor features at the edge of the display.

SUMMARY OF THE INVENTION

In one aspect, this invention provides several methods for integratingcapacitive touch sensors into a front plane laminate to produce a singlefilm ready for assembly into a display. Electrophoretic and otherbistable electro-optic media allow tighter integration of touch screensthan is possible in liquid crystal displays because the bistable natureof the electro-optic medium potentially allows multiplexing of variouselectrode structures within the display between driving the display andsensing user input. This is not possible in liquid crystal displays;since such displays need to be driven continuously, no opportunityexists for using any display structures for touch sensing.

Another aspect of the present invention provides a display provided witha proximity sensing device which detects when a user is in closeproximity to the display or, more specifically, to the screen thereof.

A third aspect of the present invention relates to incorporation ofresistive touch sensors into electro-optic displays.

A fourth aspect of the present invention relates to integration of adisplay and a key input device in an electro-optic display.

More specifically, in one aspect this invention provides anelectro-optic display comprising, in order:

-   -   a light-transmissive electrically-conductive layer, a peripheral        portion of which bears a plurality of conductive members having        a conductivity higher than that of the electrically-conductive        layer;    -   a layer of a solid electro-optic material; and    -   a backplane bearing a plurality of pixel electrodes,    -   the electro-optic display further comprising means for        controlling the potential of the plurality of conductive        members, such that the plurality of conductive members and the        light-transmissive electrically-conductive layer can serve as a        touch screen.

In another aspect, this invention provides an article of manufacture (afront plane laminate) comprising, in order:

-   -   a light-transmissive electrically-conductive layer, a peripheral        portion of which bears a plurality of conductive members having        a conductivity higher than that of the electrically-conductive        layer;    -   a layer of a solid electro-optic material;    -   a layer of a lamination adhesive; and    -   a release sheet.

In another aspect, this invention provides an electro-optic displaycomprising, in order:

-   -   a light-transmissive electrically-conductive layer, a peripheral        portion of which bears a plurality of conductive members having        a conductivity higher than that of the electrically-conductive        layer;    -   a light-transmissive electrically insulating layer;    -   a light-transmissive electrically-conductive layer;    -   a layer of a solid electro-optic material; and    -   a backplane bearing a plurality of pixel electrodes,    -   the electro-optic display further comprising means for        controlling the potential of the plurality of conductive        members, such that the plurality of conductive members and the        light-transmissive electrically-conductive layer can serve as a        touch screen.

In another aspect, this invention provides an article of manufacture (afront plane laminate) comprising, in order:

-   -   a light-transmissive electrically-conductive layer, a peripheral        portion of which bears a plurality of conductive members having        a conductivity higher than that of the electrically-conductive        layer;    -   a light-transmissive electrically insulating layer;    -   a light-transmissive electrically-conductive layer;    -   a layer of a solid electro-optic material; and    -   a layer of a lamination adhesive; and    -   a release sheet.

In another aspect, this invention provides an electro-optic displaycomprising, in order:

-   -   a light-transmissive electrically-conductive layer;    -   a layer of a solid electro-optic material;    -   a backplane bearing a plurality of pixel electrodes; and    -   first and second electrically conductive layers spaced apart        from another but capable of being deformed towards one another,        the first and second electrically conductive layers forming a        touch screen.

In another aspect, this invention provides an electro-optic displaycomprising, in order:

-   -   a light-transmissive electrically-conductive layer;    -   a layer of a solid electro-optic material; and    -   a backplane bearing a plurality of pixel electrodes, a        peripheral portion of the backplane extending outwardly beyond        the layer of solid electro-optic material, the peripheral        portion of the backplane bearing a plurality of radiation        generating means and a plurality of radiation detecting means,        the plurality of radiation generating means and plurality of        radiation detecting means together being arranged to act as a        touch screen.

BRIEF DESCRIPTION OF THE DRAWINGS

As already mentioned, FIG. 1A is a schematic cross-section through aprior art touch screen.

FIG. 1B is a schematic top plan view of the touch screen shown in FIG.1A.

FIG. 2 is a schematic cross-section through a first electro-opticdisplay of the present invention having a touch screen incorporated intothe front electrode of the display.

FIG. 3 is a schematic cross-section through a modified form of the firstelectro-optic display shown in FIG. 2.

FIG. 4 is a schematic cross-section through a second electro-opticdisplay of the present invention having a front touch screen spaced fromthe front electrode of the display.

FIG. 5 is a schematic cross-section through a modified form of thesecond electro-optic display shown in FIG. 4.

FIGS. 6 and 7 are schematic cross-sections through two differentelectro-optic displays of the present invention having front resistivetouch screens.

FIG. 8 is an exploded view of a display of the present invention havingan array of switches that are operated by physical deformation of thedisplay under pressure.

FIG. 9 shows the appearance of the display shown in FIG. 8 when it isrunning a cellular telephone program.

FIG. 10 shows the arrangement of bus lines in a non-rectangular displayof the present invention.

FIGS. 11 and 12 show the arrangement of bus lines in displays of thepresent invention provided with cut-outs to accommodate various displaycomponents.

FIG. 13 shows the appearance of a display of the present inventionrunning a program in which large buttons extend over multiple pixels ofthe display.

FIG. 14 is a schematic cross-section through a display of the presentinvention provided with a rear resistive touch screen.

FIG. 15 is an exploded view of a prior art display using an opticaltouch screen.

FIG. 16 is an exploded view, similar to that of FIG. 15, of an opticaltouch screen of the present invention.

DETAILED DESCRIPTION

As indicated above, in one aspect the present invention provides severalmethods for integrating capacitive touch sensors into a front planelaminate to produce a single film ready for assembly into a display.

As illustrated in FIG. 2, the most straightforward way to effect suchintegration is to make a single conductive layer 21 serve as both theconductive layer of the touch screen and the top electrode of thedisplay. In the structure of FIG. 2, a front substrate 22, which servesas both the substrate of the touch screen and the front substrate of thedisplay, faces a viewer 24. The low sheet resistance material 23(similar to the material 3 in FIGS. 1A and 1B) lies adjacent anelectro-optic layer (illustrated as a microencapsulated electrophoreticlayer 25) provided with pixel electrodes 26 on a backplane 27. (Althoughnot shown in FIG. 2, there is normally a layer of lamination adhesivebetween the electro-optic layer 25 and the pixel electrodes 26; theremay also be a second layer of lamination adhesive between theelectro-optic layer 25 and the conductive layer 21.) The backplane maybe of a direct drive or active matrix type, and may be rigid orflexible. Connections to the conductive layer 21 and the material 23 areeffected by edge connections using conductive adhesive, as illustratedat 28, although it should be noted that instead of the single connectionto the front electrode normally needed in prior art displays, the deviceillustrated in FIG. 2 needs five independent connections, one to thefront electrode and four to the touch sensor, as described above withreference to FIGS. 1A and 1B.

The display illustrated in FIG. 2 can be produced by only minormodification of the process for constructing an electrophoretic displayusing a front plane laminate, as described in the aforementioned U.S.Pat. No. 6,982,178. As previously described, the prior art FPL processinvolves coating an ITO/PET film (available commercially) on its ITOsurface with the electrophoretic medium. Separately, a laminationadhesive is coated on to a release sheet, and the resulting sub-assemblyis laminated to the electrophoretic medium, with the lamination adhesivein contact with the electrophoretic medium, to form a finished FPL.Removal of the release sheet and lamination of the remaining layers to abackplane bearing pixel electrodes completes the display. To produce thedisplay illustrated in FIG. 2, a closely similar process may be used,except that the low sheet resistance material 23 is printed on to theITO surface of the ITO/PET film before the electrophoretic medium iscoated thereon. The present invention extends to such a modified frontplane laminate.

Alternatively, the display shown in FIG. 2 can be produced using aninverted front plane laminate as described in U.S. Patent ApplicationPublication No. 2007/0109219 and/or a double release film as describedin U.S. Pat. No. 7,561,324. A double release film of the appropriatetime essentially comprises an electro-optic layer sandwiched between twolayers of lamination adhesive, with at least one, and preferably both,of the surfaces of the lamination adhesive layers remote from theelectro-optic layer being covered by release sheets. To produce adisplay as shown in FIG. 2 using such a double release film, firstmodifies the ITO/PET (or similar) film to provide the low sheetresistance material 23 thereon. Next, one of the two release sheets ispeeled from the double release film, and the surface of the laminationadhesive thus exposed is laminated (typically under heat and pressure)to the low sheet resistance material 23 and the conductive layer 21,thus forming an inverted front plane laminate. The remaining releasesheet is then peeled from the sub-assembly so produced, and the surfaceof the lamination adhesive thus exposed is laminated (typically underheat and pressure) to the pixel electrodes 26 on the backplane 27 toproduce the final display. This second lamination can also form theconnection 28. The order of the two laminations can be reversed ifdesired, although the order just described is generally the mostconvenient for large scale production.

The use of a double release film in this manner reduces the difficultyand/or inconvenience of coating an electrophoretic medium on to theheterogeneous surface formed by printing the low sheet resistancematerial 23 on to the ITO surface of the ITO/PET film, since laminatingan adhesive layer on the heterogeneous surface is typically easier thancoating an electrophoretic medium thereon. Also, the double releasefilm/inverted front plane laminate process provides alternative ways ofeffecting electrical connections between the front electrode 21 and thebackplane 27. If a sufficiently low resistivity conductive pathway couldbe formed around the entire edge of the active display area, the touchsensor could alternatively be formed in the backplane as part of thepixel electrode layer 10.

FIG. 3 illustrates a touch screen display of the present inventionclosely resembling that of FIG. 2 but including a color filter array 29.This color filter array is formed on the front substrate 21 and thenovercoated with a clear electrically conductive layer 22. As in thedisplay shown in FIG. 2, the only additional step needed in the displaymanufacturing process is printing the low sheet resistance material 23on to the electrically conductive layer 22. It will be appreciated thatthe display shown in FIG. 3 can be produced using a double releasefilm/inverted front plane laminate process exactly analogous to thatalready described with reference to FIG. 2.

FIG. 3 also illustrates an alternative method of establishing electricalconnections to the low sheet resistance material 23 and to theelectrically conductive layer 22. Instead of the edge connections shownin FIG. 2, the display of FIG. 3 uses a flexible circuit tail 30 bondedor adhered to the connection pads 6 (see FIG. 1B) of the touch screen.The flexible circuit tail 30 connects to the touch screen controllerindependently from the backplane (although it could alternativelyterminate on the backplane itself, and thence be connected to thecontroller). The circuit tail 30 thus eliminates the need for a separateconnection between the front electrode of the display and the backplane,thus potentially simplifying display construction.

The displays shown in FIGS. 2 and 3 add touch screen functionality tothe display with very little additional cost and no impact to opticalperformance or thickness. The size of the peripheral region between theactive area and the physical edge of the display is, however, increased.In both displays, the sensing and display driving phases are distinct intime. During display driving, a common driver circuit would havepriority and would be connected to the front electrode, possibly throughthe touch screen components. When display driving is completed, thecommon driver circuit can be disabled or disconnected and the touchscreen controller connected to the display. Some provision, using analogor transistor switches, will be required to isolate each of the twoparts of the circuit when they are not active.

In displays such as those illustrated in FIGS. 2 and 3, where the samefront electrode serves as both a driving and a sensing electrode, onepotential issue is perturbation of the electro-optic layer by thesensing signals on the top electrode during the touch sensing phase ofoperation. Sensing signal levels are typically in the 2-3 V range at thecorners, which is enough to cause problems in electrophoreticelectro-optic layers, either by partial driving or by more subtledegradations of image stability. There are several ways to minimize oreliminate this problem.

Sensing signal frequencies are typically of the order of 10 kHz range,and may thus be high enough not to affect many electro-optic media. Itmay also be advantageous to have the sensing signal centered around 0 V,so that it is DC balanced. This could be done by changing the outputstage of the touch sensor controller, dereferencing the ground of thecontroller, or by AC coupling the signals through relatively largecapacitors between the controller and the panel electrodes.

Another approach is to allow the pixel electrodes to float (i.e., notapply any driving voltage) during the sensing phase. In an active matrixdisplay, this can be done by keeping one rail of the gate drivers onduring the sensing phase, thus keeping the transistors non-conductiveand allowing the pixels to float individually, and limiting the electricfield experienced by the electro-optic layer. Alternatively, the sourcelines of the array (or the drive lines in a direct drive case display)can be driven with the sensing waveform with the gate drivers all turnedon, but implementation of this approach poses practical difficulties.

If the difficulties posed by electrical interference between displaydriving and touch sensing are deemed too great, or if concurrent oroverlapping display driving and touch sensing are necessary to allow forrapid response, as for example in a drawing operation or during fasttyping of text input with rapid updating of the display, other forms ofintegration of a touch sensor into an electro-optic display may be used.

FIG. 4 illustrates one form of such integration, in which the touchscreen components are placed on the opposite side of the front substratefrom the electro-optic layer, thus separating the sheet conductor 22 ofthe touch screen from the front electrode of the display. This allowsthe touch screen sheet conductor can use a material to higher sheetresistance than is desirable for the front electrode of a display, sothat the touch screen sheet conductor can be formed of an inexpensive,highly light-transmissive material such as very thin ITO or a conductivepolymer. Such a conductive polymer may, in some cases, be appliedinexpensively, prior to coating of the electro-optic medium, on to thenon-ITO-coated surface of the ITO/PET film in roll form used to preparefront plane laminates, as discussed above, without significant reductionin the light transmission by the film. After a front plane laminateprepared in this manner has been severed into pieces required for aparticular size of display, the layer 23 required for the touch screencan be applied.

FIG. 4 illustrates the connections to the touch screen being made via aflexible circuit tale 30, which connects to both the touch screen andthe front electrode, thus eliminating the need for a separate connectionfrom the front electrode to the backplane. Alternatively, multilayerscreen printing techniques with vias could be used to provideconnections between the touch screen and the backplane.

FIG. 4 also illustrates a protective sheet 31 which is typicallylaminated on top of the front substrate using optically clear adhesive(not shown). The protective sheet 31 is designed to give the display themechanical durability required for its intended use, and can incorporateultra violet barriers and diffuse reflective hard coats to provide anattractive and durable front surface on the display. In the display ofFIG. 4, the protective sheet also serves to encapsulate and protect thetouch screen layers.

The display shown in FIG. 4 can be produced using a modified front planelaminate or a modified double release film/inverted FPL process exactlyanalogous to those previously described in connection with the displayof FIG. 2. To produce the display of FIG. 2, the substrate used toproduce the front plane laminate, or the substrate to which the doublerelease film is laminated, may be modified to provide the frontelectrically-conductive layer 22 and the low sheet resistance material23 thereon. The protective sheet 31 may also be attached to thesubstrate at this point, but is typically more conveniently attached ata later stage in the production process.

An alternative to the structure shown in FIG. 4 uses a multilayerconductive coating with intervening dielectric layers on one side of thefront substrate 21; within this multilayer conductive coating, aconductive layer closer to the viewing surface of the display can beused as part of the touch screen, while a conductive layer closer to theelectro-optic medium would serve as the front electrode of the display.Even a thin dielectric layer interposed between these two conductivelayers would block direct current transmission and, at least to someextent, isolate the display driving and touch sensing electrical signalsfrom one another.

Finally, FIG. 5 illustrates a modification of the display of FIG. 4 inwhich the layer 23 of the touch screen is disposed on the inward surfaceof the protective sheet 31. In such a display, it will typically beadvantageous for the front electrode to connect to the backplane via aedge connector 28, while the touch screen connections pass through aflexible tail 30. Note that the display of FIG. 5 can be produced bymodifying only the protective sheet used in the display, and thus mayprovide a relatively easy path to retrofit an existing design ofelectro-optic display with a touch sensor when desired.

As already mentioned, a second aspect of the present invention relatesto a display provided with a proximity sensing device which detects whena user is in close proximity to the display or, more specifically, tothe screen thereof. When a surface capacitive touch sensor is used witha small to medium format display, a proximity sensor is typically neededto determine when the user approaches the display screen and to providea common mode signal to assist in filtering of the signals from the fourcorner sensors which, as described above with reference to FIG. 1B, formpart of the touch screen. Also, if a battery-driven display uses abistable electro-optic medium, it is desirable, in order to extendbattery life, to shut down power to most parts of the display when theuser is not interacting with the display and the display is not beingrewritten. A method to detect an approaching user is thus a usefulinput.

As indicated above in the discussion of the display shown in FIGS. 1Aand 1B, a proximity sensing electrode is a standard feature of mostsurface capacitive touch screens. This second aspect of the presentinvention relates to methods for providing proximity sensing as part ofthe backplane of an electro-optic display, or making use of existingbackplane features to provide this capacity, together with ways forusing proximity sensing in a portable display system using a bistableelectro-optic medium. Using a backplane feature to provide proximitysensing in combination with a touch screen provided on the front planeof the display can lead to a smaller border size for the touch screen,and potentially a lower construction cost. (The term “front plane” of adisplay is used herein in its conventional meaning in the art to referto the electro-optic layer and all layers of the display between theelectro-optic layer and the viewing surface.)

Many electro-optic displays include a border or peripheral electrode, adirectly driven electrode positioned around the active area of thedisplay and usually 1 to 3 mm in width. This border electrode serves asa single pixel which ensures that the entire edge of the display is inthe same optical state. Without such a border pixel, the address linesextending across the peripheral portion of the display can capacitivelyswitch the electro-optic material above them, producing distractingvisual effects. The border electrode also provides some tolerance inpositioning the display screen relative to a bezel of a housing.

In a display using a bistable electro-optic medium, the border electrodecan be used, by time division multiplexing, both to address theoverlying peripheral portion of the electro-optic medium and as aproximity sensing device. Switches, either analog or field effecttransistor, could be used to isolate the circuits for these twofunctions from one another, or it may be possible to design the relevantcircuits so that they do not interfere with one another.

Alternatively, dedicated electrodes for the proximity sensor could beprovided on backplane. Although such dedicated electrodes might increasethe optically inactive areas at the periphery of the backplane,including such dedicated electrodes would be inexpensive since there arealready multiple patterned conductor layers on commercial backplanes.

The foregoing proposals assume that a touch screen is built into thefront plane of the display. If only proximity sensing is desired and nottouch screen capability, the front electrode of the display can be timedivision multiplexed between driving the display and sensing proximity.FIG. 1B and the related description above describe this approach toproviding both proximity sensing and touch screen capabilities, but ifonly proximity detection is desired, no additional physical features areneeded in the display beyond those inherently present; in other words,additional circuitry on the display controller can provide anyelectro-optic display with proximity sensing capability when theelectro-optic medium is not being driven.

Proximity sensing has uses in bistable displays other than those forwhich such sensing is employed in non-bistable displays. It is desirablethat a battery-driven portable bistable display device shut down powerto most of the internal systems (i.e., enter a deep sleep mode) when theimage on the display is static and there is other device activity.However there is often a significant latency time associated with wakingup from a deep sleep mode, especially when powering up a displaycontroller and charging bias supplies is required. Using any of theabove techniques, the device use proximity sensing to detect a userapproaching and begin the wakeup process expecting that the user willsoon wish to interact with the device. Another use could be to refreshan image long present on a screen, and hence somewhat faded, as a userapproaches.

Such a sensor could also form a one bit input device for device's userinterface; for instance a prompt could say “tap screen to accept”, or inan electronic book reader tapping the screen could advance the page.Many display device designs provide two separate connections to thecommon front electrode, and appropriate control circuits can use the twoseparate connections as a rudimentary differential proximity sensor.Such a sensor could be used so that, for example, a tap on one side ofthe screen advances a page and on the other side moves back a page.

As already noted, a third aspect of the present invention relates toincorporation of resistive touch sensors into electro-optic displays. Ina conventional resistive touch sensor, two continuous conductive filmsare separated by an air gap; the spacing between the conductive films ismaintained by mechanical spacers placed between them. One film(typically called the “bottom film”) is placed on a rigid support, whilethe other (“top”) film is on a deformable substrate. Voltages areapplied to the bottom film by means of electrodes along its edges,creating a voltage gradient across the film. When the top film isphysically deformed by applied pressure, it comes into contact with thebottom film, creating an electrical circuit between the two layers. Bydetecting the voltages on the top film by means of electrodes placed atthe edges of the top film, the location of the contact in the x and ydimensions can be determined. More elaborate arrangements of electrodescan improve the accuracy of the sensing, especially for larger panels.In some cases, it may even be possible to measure the force of thetouch, to the degree that it affects the size of the contact areabetween the films.

Resistive touch screens have several key advantages over other competingtechnologies, including low cost, robustness, and sensitivity to anykind of mechanical touch (some other touch sensors only respond to aspecial stylus, or a human finger). One major disadvantage, however, isthe loss in brightness and contrast of the display, as in a reflectivedisplay the presence of a resistive touch sensor requires that lightreflected from the electro-optic medium make two passes through twoadditional films. Other disadvantages are the thickness and weight addedby the resistive touch system, in which the rigid support must be rigidenough not to deflect when pressure is applied to the front film. Thisis especially important in liquid crystal displays, the opticalproperties of which are markedly affected by pressure.

It has been found that, in an electro-optic display, the rigid supportof prior art resistive touch sensors can be replaced by a thin andpossibly flexible polymeric film, with the rigidity necessary for theoperation of the touch sensor being provided by a rigid displaybackplane underlying this thin polymeric film.

An electro-optic display of the present invention having this type ofresistive touch sensor is illustrated in schematic cross-section in FIG.6 of the accompanying drawings. This display comprises (in order fromthe backplane to the viewing surface), a rigid substrate 40, a thin filmtransistor active matrix backplane 42, a layer 44 of a solidelectro-optic medium (illustrated as an encapsulated electrophoreticmedium), a front electrode 46, a transparent substrate 48, a transparentconductive layer 50, which acts as the bottom film of the resistivetouch sensor, an air gap 52 defined by spacers 54, a transparentconductive layer 56, which acts as the top film of the resistive touchsensor, and an optically transparent flexible substrate or protectivelayer 58, which serves to prevent mechanical damage to both theresistive touch sensor and the electro-optic medium.

A further electro-optic display having a resistive touch sensor isillustrated in FIG. 7 of the accompanying drawings. The display of FIG.7 may be regarded as a modification of that shown in FIG. 6, the singletransparent substrate 48 shown in FIG. 6 being replaced by two suchsubstrates 48A and 48B adhered to each other by a thin, optically clearadhesive layer 60. It will be seen from FIG. 7 that each of thesubstrates 48A and 48B bears only a single transparent conductive layer,thus avoiding the need for providing transparent conductive layers onboth sides of a single sheet.

The displays shown in FIGS. 6 and 7 can readily be produced using amodified form of the front plane laminate described above with referenceto U.S. Pat. No. 6,982,178, in which the front substrate of the frontplane laminate is modified to include a second light-transmissiveelectrically-conductive layer on the opposed side of the front substratefrom the release sheet. To produce the electro-optic display of FIG. 7,the modified front substrate may be produced by adhesively securingtogether two separate substrates each provided with onelight-transmissive electrically-conductive layer. The secondlight-transmissive electrically-conductive layer may optionally bepatterned, by screen printing or other process, to provide featuresneeded for its eventual role as the bottom film of the resistive touchsensor. This conductive layer may also be provided with an array ofmechanical spacers which will form the spacers 54 in the final display.

The displays shown in FIGS. 6 and 7 can also be modified to use asomewhat flexible backplane, one that can be curved with a large radiusof curvature, but still provides enough resistance to mechanicaldeformation to allow proper operation of the resistive touch sensor.Such a backplane may be based upon a thin metallic foil, as describedfor example in U.S. Pat. No. 6,825,068 and Publication No. 2004/0180476.

The displays with resistive touch sensors provided by this aspect of thepresent invention possess cost advantages since they remove one or moreof the components and manufacturing steps necessary to incorporate aconventional resistive touch sensor into an electro-optic display, andalso possess improved optical performance since elimination of one ormore of the layers of a conventional resistive touch sensor improves theoptical transparency of the display and decreases the haze thereof, thusimproving the dark state of the display. Finally, the displays of thepresent invention offer reduced thickness and weight of the display byremoving the need for the conventional thick heavy bottom substrate.

As already mentioned, a fourth aspect of the present invention relatesto integration of a display and a key input device in an electro-opticdisplay. It has long been realized that the type of dedicated,permanently marked keyboard traditionally used in desktop and laptopcomputers is, by virtue of its size, weight and permanent markings,disadvantageous for use in small portable electronic devices.Accordingly, many electronic devices are now available in which akey-based input function is integrated into the display. For example,Apple's iPhone (Registered Trade Mark) eliminates the traditional keypadin favor of a liquid crystal display equipped with a resistive touchscreen. Phone numbers, text messages and other data are entered bycontacting an area of the screen delineated by a portion of an image,and interpreted by software.

This kind of “soft” or “virtual” keyboard offers distinct advantagesover a traditional keypad, in that the indicia on and/or the locationsof the virtual keys can be easily changed by software, this allowing thedevice to transform the function of the various keys depending onfactors such as the local language (different character sets), vision ofthe user (large text), or the application being used (for example,letters for text entry, numbers for dialing, and special sets of glyphsfor particular programs, as for instance when audio or video programsmimic the glyphs conventionally used on dedicated audio or videoequipment). In addition, since in conventional cellular telephones andsimilar portable electronic devices, the display and the keypad eachtake up about one-half of the usable surface area of the device,elimination of the dedicated keypad in favor of a virtual keyboardenables one to roughly double display size without increasing theoverall size of the device.

However, many users complain of the lack of tactile feedback fromvirtual keyboards. If a user is trying to dial a telephone number whileaccomplishing another task, such as driving, the flat surface of thedisplay does not offer any clue, other than visual, as to the locationsof the keys, or any tactile or audible feedback to indicate when a keyhas been pressed. This makes it more difficult to dial a telephonenumber quickly and accurately on a featureless touch screen, and similardifficulties are encountered with other types of input sequences. It isalmost impossible to touch type on a virtual keyboard without tactilefeedback.

U.S. Patent Application Publication No. US 2003/0058223 describes adeformable display that is placed over an array of membrane switch“popples”. Mechanical pressure on the display surface is transmittedthrough the display to activate the underlying switches, which exhibit anonlinear force profile as they are deformed (a “click”) However, thespecific embodiments describe only a keypad equipped with a segmenteddisplay capable of displaying a limited set of key labels by directdrive of electrodes.

The present invention provides an electro-optic display comprising anactive matrix display overlying an array of switches (keys) that areoperated by physical deformation of the display under pressure. Theactive matrix display displays not only indicia for the keys by also allother data required to be displayed by the application being run, andthus serves as the main screen of the electro-optic display.

FIG. 8 of the accompanying drawings is an exploded view of oneembodiment of such a display. As seen in that Figure, the displaycomprises a rear substrate 80 provided with an array ofpressure-sensitive switches 82. Overlying the rear substrate is aflexible membrane 84 having raised areas 86 aligned with the switches82. The next, optional, layer of the display comprises an array ofsquare keys 88 which assist in ensuring that pressure on any area of thedisplay is transmitted to the closest switch 86. Overlying the keys 88is a flexible TFT array 90, a front plane 92 (comprising an adhesivelayer, electro-optic layer and front electrode layer, none of which areshown separately in FIG. 8) and an (optional) protective sheet 94.

FIG. 9 shows the appearance of the display shown in FIG. 8 when it isrunning a cellular telephone program. A U-shaped area extending aroundthe side edges and the top edge of the display shows the digit 0-9. Thecentral portion of the display shows a list of memorized telephonenumbers. The lower portion of the display shows icons for dialing ahighlighted telephone number from the list and for other functionscommon to cellular telephones.

Typically, the display itself would comprise a rectilinear array ofpixels, each connected to a data bus line by an individual thin filmtransistor (TFT), controlled by a gate bus line. The TFT array should beconstructed on a material that can deform under pressure to activate theunderlying keys, for example, PET, polyimide, PEN, or a thin metalsubstrate, e.g. stainless steel foil.

Prior art TFT arrays are typically square or rectangular since this formof array has the advantage of allowing the display area to be addressedwith as few bus lines as possible. However, it may be desirable fordesign reasons to create a display that includes cut-outs for amicrophone or speaker, rounded edges, or other non-rectangular designs.Accordingly, the present invention extends to displays in which thepixel array is non-rectangular and/or includes interior holes. FIG. 10illustrates a non-rectangular display, in which data lines 100 aresuccessively dropped as the width of the display decreases upwardly (asillustrated), while the lengths of the gate bus lines 102 aresuccessively decreased to match the decreasing width. FIGS. 11 and 12show two examples of displays with through-holes 110. In FIG. 11 sourcelines 112 are routed around the hole 110 to activate non-contiguoussections of the same column, and separate gate lines are provided forthe left and rights sides of the display where the gate liens aredivided by the hole 110. Similarly, in FIG. 12 gate lines 114 are routedaround the hole 110 to activate non-contiguous sections of the same row,and separate source lines are provided for areas above and below thehole 110 where the source lines are divided by the hole.

In some displays of the present invention, the user interface mayrequire only one or two coarse inputs (for example, yes/no). In such acase, it may be convenient to provide an operating mode of the devicewhere activation of any one of the keys within a pre-defined areaproduces the same result. Furthermore, the image on the display mayoutline the physical boundaries of the set of keys that are mapped tothe same result. A display of this type is illustrated in FIG. 13, wherelarge “YES” and “NO” buttons 130 and 132 respectively each extend overfour of the underlying pixels 134.

Since the present invention eliminates the need for a keypad separatefrom the display, the display can cover the majority of the devicesurface. In the case of a so-called “candy bar” cellular telephone,which is long, thin and not hinged, the display may cover one entiremajor surface of the telephone. In the case of a clamshell telephone,which folds in half along the short axis of the phone, thedisplay/keyboard may be split into two units, each covering one half ofthe face. Alternatively, the display itself may be made of flexiblematerial and incorporate a bend window that allows it to fold in halfalong a line coincident with the telephone's hinge, thus giving theappearance, when the telephone is opened, of a single large displaycovering the face of the telephone.

The touch screen displays shown in FIGS. 6 and 7 above use an air gapfront touch screen (i.e., a touch screen which relies upon an air gapbetween two conductive layers and which is positioned between theelectro-optic layer and the viewing surface of the display). Resistivetouch sensors can also be constructed of two patterned electricallyconductive films separated by a variably resistive material. When thevariably conductive material is deformed by applied pressure, itsresistance changes; detection of the location and magnitude of thischange in resistance by a controlling device will indicate the locationand intensity of touch applied to the system. Also, when the appearanceof the electro-optic medium used is not significantly affected by manualpressure (as in encapsulated and especially polymer-dispersedelectrophoretic media), the touch screen can be placed behind theelectro-optic layer (i.e., on the opposed side of the electro-opticlayer from the viewing surface of the display.

An example of such a touch screen display is shown in FIG. 14. In thisdisplay, the substrate 40, the backplane 42, the electro-optic layer 44,the front electrode 46 and the front substrate 48 are all essentiallyidentical to the corresponding parts of the displays shown in FIGS. 6and 7. However, the display shown in FIG. 14 further comprises an upperconductor 150 of a resistive touch sensor, this upper conductor beingpatterned into columns, a variably resistive material 152 (typically aliquid), a lower conductor 154 and a lower substrate 156. Although notshown in FIG. 14, the lower conductor 154 is patterned into rows runningperpendicular to the columns of upper conductor 150.

Resistive touch sensors that incorporate a variably resistive materialtypically do not require a large amount of deflection to activate, andthus can be placed behind the backplane of the electro-optic display. Inthis position, the touch sensor may be activated with pressure appliedthrough the electro-optic display stack as shown in FIG. 14. Advantagesof this configuration are that the optically lossy film of the resistivetouch sensor is not present between the electro-optic layer and the userviewing the display, so that the contrast ratio and reflectivity of the“naked” display (i.e., the display without the touch sensor) aremaintained.

Another touch screen technology which can usefully be used withelectro-optic displays is optical touch screen technology, usually inthe form of infra-red touch screen technology. (Since optical touchscreen technology involves passing beams of radiation across the viewingsurface of the display, it is desirable that the radiation used beoutside the visible range in order to ensure that no visible streaks ofradiation are present on the viewing surface.) However, hitherto theimplementation of such optical touch screen technology in electro-opticdisplays has been rather cumbersome and costly.

As illustrated in FIG. 15, the prior art implementation of optical touchscreen technology has typically involved providing the display with alight-deflecting bezel 160, an electro-optic module 162 (which includesthe electro-optic layer itself, the front substrate, front electrode andbackplane), and a separate rectangular circuit board 164. The circuitboard 164 extends outwardly beyond the electro-optic module 162 so thata peripheral portion of the circuit board 164 is exposed, and along twoedges of this peripheral portion are arranged infra-red light emittingdiodes (LED's) 166, while the other two edges of the peripheral portioncarry photodiodes 168 sensitive to the radiation emitted by the LED's166. The light-deflecting bezel 160 bears light-deflecting surfaces (notshown) such that radiation emitted from the LED's 166 travelsperpendicular to the plane of the circuit board 164, is deflected by thebezel 160 so that it travels across and parallel to the viewing surface(the upper surface as illustrated in FIG. 15) of the electro-opticmodule 162, and it again deflected by the bezel downwardly on to thephotodiodes 168. Thus, any object which obstructs the radiation passingacross the viewing surface will result in the IR radiation failing toreach at least two of the photodiodes 168, thereby enabling the positionof the object to be detected in two dimensions.

FIG. 16 shows an IR optical touch screen display of the presentinvention. This display has a light-deflecting bezel 160 identical tothat shown in FIG. 15. However, the display of FIG. 16 does not requirea discrete circuit board; instead, the backplane of the electro-opticmodule 162 is made larger than the corresponding module in FIG. 15. Morespecifically, although not shown in FIG. 16, the backplane of theelectro-optic module is made larger than the electro-optic layer itself,so that a peripheral portion of the backplane is exposed, on thisperipheral portion of the backplane bears LED's 166 and photodiodes 168which function in the same manner as the corresponding integers in FIG.15.

The LEDs 166 and photodiodes 168 in FIG. 16 can be mounted directly onthe electro-optic module and are adhered to the glass or other backplaneusing a z-axis conductive adhesive. Electrical connections to the LEDsand photodiodes can be deposited on the backplane using traditional TFTmetal layer deposition techniques already used for forming otherconnection on the backplane, for example those use to connect the rowand column drivers of a backplane to the row and column electrodes of anactive matrix backplane.

Photodiodes can be constructed such that they have a single wire serialinterface whereby one diode sends its data to the next who then appendsits own data to that received from the previous photodiode. In thismanner the number of connections to the photodiode array can beminimized.

It will be apparent to those skilled in the art that numerous changesand modifications can be made in the specific embodiments of theinvention described above without departing from the scope of theinvention. Accordingly, the whole of the foregoing description is to beinterpreted in an illustrative and not in a limitative sense.

The invention claimed is:
 1. An electro-optic display comprising, inorder: a light-transmissive electrically-conductive layer; a layer of asolid electro-optic material; and a backplane bearing a plurality ofpixel electrodes, a peripheral portion of the backplane extendingoutwardly beyond the layer of solid electro-optic material, theperipheral portion of the backplane bearing a plurality of radiationgenerating means and a plurality of radiation detecting means, theplurality of radiation generating means being arranged to directradiation across the light-transmissive electrically-conductive layer ofthe display, and the plurality of radiation detecting means beingarranged to detect radiation from the plurality of radiation generatingmeans that has passed across the light-transmissiveelectrically-conductive layer of the display so that the plurality ofradiation generating means and plurality of radiation detecting meanstogether act as a touch screen.
 2. An electro-optic display according toclaim 1 wherein the radiation generating means comprises a plurality oflight emitting diodes emitting in the infra-red region.
 3. Anelectro-optic display according to claim 1 wherein the radiationdetecting means comprises a plurality of photodiodes.
 4. Anelectro-optic display comprising, in order: a light-transmissiveelectrically-conductive layer; a layer of a solid electro-opticmaterial; and a backplane bearing a plurality of pixel electrodes, aperipheral portion of the backplane extending outwardly beyond the layerof solid electro-optic material, the peripheral portion of the backplanebearing a plurality of radiation generating means and a plurality ofradiation detecting means, the plurality of radiation generating meansbeing arranged to direct radiation across the light-transmissiveelectrically-conductive layer of the display, and the plurality ofradiation detecting means being arranged to detect radiation from theplurality of radiation generating means that has passed across thelight-transmissive electrically-conductive layer of the display so thatthe plurality of radiation generating means and plurality of radiationdetecting means together act as a touch screen, the display comprising alight-deflecting bezel arranged to deflect radiation from the radiationgenerating means across the light-transmissive electrically-conductivelayer, and thence on to the radiation detecting means.
 5. Anelectro-optic display according to claim 4 wherein the electro-opticmaterial comprises an electrophoretic material comprising a plurality ofelectrically charged particles disposed in a fluid and capable of movingthrough the fluid under the influence of an electric field.
 6. Anelectro-optic display according to claim 5 wherein the electricallycharged particles and the fluid are confined within a plurality ofcapsules or micro cells.
 7. An electro-optic display according to claim5 wherein the electrically charged particles and the fluid are presentas a plurality of discrete droplets surrounded by a continuous phasecomprising a polymeric material.
 8. An electro-optic display accordingto claim 5 wherein the fluid is gaseous.